Tips are not just random, quick missions for getting XP--they actually work toward a couple of other goals in-game besides experience.

Reason #1: The Hero Merit

One big reason to play tips is because of a little reward called a "Hero Merit." As a Hero in City of Heroes, if you complete 10 Tip Missions that are aligned with "heroic" motivations, you will be allowed to play a Heroic "Morality" mission, which reaffirms your "Hero" status, and empties out your Tip credits so you can build up more credits.

The first time you complete a Morality mission, you will receive 50 reward merits; every time after that, you will receive one Hero Merit, which you can trade in Fort Trident. Trading in your Hero Merits nets you many awesome rewards, detailed on the How the Tip System Works page.

Reason #2: Changing Your Alignment

Another reason to play tips is if you are trying to transfer your character from heroside to villainside. If you want to do that, check out the Changing Alignment with Tip Missions page.